This invention relates to a mechanical pressing machine provided with a dynamic balancing device for balancing an unbalanced inertia force of a reciprocally-moving slider driven by a rotation cam. One known example of mechanical press utilizing a rotation cam is the type of press utilizing a constraint cam such as a yoke mechanism. In such a press, a slider is connected to a follower through a connecting rod, and a rotational motion of the cam is converted into a linear reciprocal motion of the slider. In such a press utilizing the rotation cam, when the operation is started, vibrations, resulting from an unbalanced inertia force due to a reciprocal movement of the slider, develop to produce noises and to cause a positional error, as in a conventional crank press. To avoid this, usually, a dynamic balancing device has been used.
In a conventional dynamic balancing device, an unbalanced inertia force of the reciprocating slider is canceled by a balance weight which is equivalent in weight to the slider, and is connected through a cam or links, supported on a frame, at a position in opposite phase with crests of a cam. With this construction, the unbalanced inertia force in the whole of the press is canceled by the balance weight, and therefore vibrations of the press itself (except for the slider and the moving parts) are reduced,, thereby enabling a high speed operation of the press.
In the above conventional pressing machine, however, directing attention to the slider having an upper die mounted thereon, an inertia force F, produced during the reciprocal movement, produces a flexure S=F .times.K in accordance with the rigidity (spring constant) K of a propagation path (generally extending from a follower via a driver to a press frame) of a load. Generally, this flexure S becomes maximum in the vicinity of a lower dead center, and the dimension of the slider is expanded downward, thus adversely affecting the precision at the lower dead center. And besides, this flexure S is proportional to the inertia force, and therefore is increased as the speed increases. Thus, conventionally, although the pressing machine is apparently rendered quiet by the provision of the dynamic balancing device, this has been found not entirely satisfactory from the viewpoint of the dynamic precision such for example as a lower dead center precision and a coining precision.